The present invention relates to a method for decomposing halogenated hydrocarbon gas and an apparatus therefor, particularly relates to a method and an apparatus for efficiently decomposing and detoxifying ozone layer destruction materials such as chlorofluorocarbons specified by relating laws.
Halogenated hydrocarbons include organic chlorine base solvents and chlorofluorocarbons. They are generally stable in terms of chemical and thermal, soluble in oil, and highly volatile. Owing to these properties, they are consumed in various industrial sectors in large quantities. For example, organic chlorine base solvents are used as washing liquids in dry cleaning and as degreasing washing agents for metals, and chlorofluorocarbons are used as coolants in air conditioners and as resin foaming agents. Once, however, they are released to atmosphere, they induce serious environmental problems such as ozone layer destruction and global warming. Furthermore, some of them are identified to cause carcinogenesis and teratogenesis in human body.
There have been proposed various kinds of technologies for decomposing and treating them as means to avoid these problems. For instance, JP-A-10-180040, (the term xe2x80x9cJP-Axe2x80x9d referred herein signifies the xe2x80x9cunexamined Japanese patent publicationxe2x80x9d), discloses a method for decompose chlorofluorocarbon gas by combusting it with hydrogen, methane, and the like mixing there together. According to the method, a supporting gas such as methane and hydrogen is added to the chlorofluorocarbon gas in a cylindrical burner to improve the combustibility, while mixing these components in a swirling flow pattern to homogenize the combustion, (the combustion method).
According to a method disclosed in JP-A-9-276691, chlorofluorocarbons are hydrolyzed in a high frequency plasma decomposition furnace, and the generated carbon dioxide and hydrogen are combusted by introducing air there into, (the plasma decomposition method).
According to a method disclosed in JP-A-10-180040, a gas that contains organic chlorine compounds is introduced to pass through a plurality of ultraviolet ray irradiation reactors structured by a combination of complete mixing and incomplete mixing types, thus attaining efficient photo-decomposition treatment, (the UV decomposition method).
According to a method disclosed in JP-A-8-38853, halogen-containing waste is decomposed by hydrolysis under the presence of super-critical water at high temperature and high pressure and by oxidation decomposition reaction using an oxygen-containing fluid, (the super-critical water decomposition method).
According to a method disclosed in JP-A-6-343827, contacting with a catalyst made of silicon carbide that supports platinum efficiently decomposes a gas that contains chlorofluorocarbons. The use of platinum-supporting silicon carbide as the catalyst carrier improves corrosion resistance to hydrogen chloride generated during the decomposition of the chlorofluorocarbons, thus assuring long period of stable catalyst activity.
As of the above-described prior art, the combustion method, the plasma decomposition method, the UV decomposition method, and the super-critical water decomposition method cannot be said as satisfactory methods for detoxifying halogenated hydrocarbon gas in large quantities, efficiently, and safely, though they show a certain level of decomposition treatment effect to haloganated hydrocarbons. For example, the combustion method requires high temperatures of 700xc2x0 C. or above, and raises problems that free halogen forms severely corrosive gases (hydrogen fluoride, hydrogen chloride, and the like) to corrode the combustion furnace. Furthermore, the method has a difficulty in temperature control. The plasma decomposition method is high in running cost relating to electricity and plasma gas, which induces economical problem. The UV decomposition method has a limit of scale up of UV lamp and of quartz jacket, so that the method is not suitable for treating large quantity of gas. The super-critical water decomposition method requires high temperatures of 400xc2x0 C. or above and high pressures of 320 atm or more.
Contrary to these technologies, the catalyst decomposition method has advantages of effective treatment at a relatively low temperature and of simple treatment apparatus. However, the catalyst used in the catalyst decomposition method is generally expensive, so that, once catalyst degradation is generated caused from non-uniform heating of catalyst by an external heating electric heater, the frequency of catalyst replacement increases to decrease the economy. In addition, when a metal is used as the catalyst carrier, the halogen-containing gas such as halogenated hydrogen gas may degrade the carrier.
The inventors of the present invention conducted detailed analysis of a decomposed gas, which was generated during the catalyst decomposition using an external heating electric heater as the heating source, and found that dioxins existed in the decomposed gas.
The present invention has been completed responding to the above-described situation. And an object of the present invention is to provide a method and an apparatus for decomposing haloganated hydrocarbon gas, which method and apparatus decompose halogenated hydrocarbon gas economically and stable, in large quantities, without generating dioxins, without relying on any special treatment.
To solve the above-described problems, the present invention provides the following-described method and apparatus.
Firstly, the present invention provides a method for decomposing halogenated hydrocarbon gas in a gas that contains the halogenated hydrocarbon gas. The method comprises the step of supporting a catalyst for decomposing the halogenated hydrocarbon gas on a carrier, which is electrically conductive and is resistant to halogen-containing gas. Furthermore, the first method comprises the step of decomposing the halogenated hydrocarbon gas by letting the gas that contains the halogenated hydrocarbon gas pass through the carrier, while heating the carrier by electromagnetic induction heating.
In the method for decomposing halogenated hydrocarbon gas, the carrier preferably comprises at least one material selected from the group consisting of SiC and stainless steel.
In the method for decomposing halogenated hydrocarbon gas, the catalyst preferably comprises at least one element selected from the group consisting of Pt, Pd, Au, Rh, and Ni.
In the method for decomposing halogenated hydrocarbon gas, the catalyst preferably comprises at least one element selected from the group consisting of W, Cr, Fe, Mo, and V.
In the method for decomposing halogenated hydrocarbon gas, the catalyst preferably comprises: at least one element selected from the group consisting of Pt, Pd, Au, Rh, and Ni, and/or at least one element selected from the group consisting of W, Cr, Fe, Mo, and V; and titania (TiO2).
Secondly, the present invention provides a method for decomposing halogenated hydrocarbon gas. The method comprises the step of decomposing a halogenated hydrocarbon gas by letting a gas that contains the halogenated hydrocarbon gas pass through a heating body which is resistant to halogen-containing gas and is electrically conductive, while heating the heating body by electromagnetic induction heating.
In the method for decomposing halogenated hydrocarbon gas, the heating body is preferably a structure made of at least one material selected from the group consisting of SiC and stainless steel.
Thirdly, the present invention provides an apparatus for decomposing halogenated hydrocarbon gas. The apparatus comprises a carrier which supports a catalyst for decomposing the halogenated hydrocarbon gas, which is resistant to halogen-containing gas and is electrically conductive, and which allows a gas that contains halogenated hydrocarbon to pass through there. Furthermore, the apparatus comprises a heating mechanism to heat the carrier by electromagnetic induction heating.
Fourthly, the present invention provides an apparatus for decomposing halogenated hydrocarbon gas. The apparatus comprises a heating body which is resistant to halogen-containing gas and is electrically conductive, and which allows a gas that contains halogenated hydrocarbon gas passing through there. Furthermore, the apparatus provides a heating mechanism to heat the heating body by electromagnetic induction heating.
The inventors of the present invention speculated that the generation of dioxins in the conventional catalyst decomposition method is caused by the following reasons. That""s to say, the external heating electric heater used as the heating means is difficult to cool the decomposed gas owing to the radiant heat thereof, and the decomposed gas is held at a temperature level of dioxin re-synthesis temperatures. Thus, the inventors of the present invention expected that the use of an electromagnetic induction heating method as the heating method that can perform rapid heating and rapid cooling prevents that kind of disadvantage. That is, since the electromagnetic induction heating method is able to perform rapid heating and rapid cooling, the dioxin re-synthesis temperature zone can be passed within a short time, thus preventing the re-synthesis of dioxins. In addition, the electromagnetic induction heating allows uniform heating so that the occurrence of catalyst degradation caused by non-uniform heating is prevented. Furthermore, the use of a catalyst carrier, which is resistant to halogen-containing gas, allows performing detoxification that decomposes halogenated hydrocarbon gas for a long period. Furthermore, sole electromagnetic induction heating, not applying any special treatment, allows treating large quantity of gas, economically.
Combustion and oxidation without using catalyst can decompose halogenated hydrocarbon gases. Accordingly, as described above in a part, when a heating body through which the gas passes is installed, instead of the catalyst carrier, and when the heating body is heated by electromagnetic induction heating to combust and oxidize to decompose the halogenated hydrocarbon gas, similar effect with the use of a catalyst can be attained.